Delaying Recovery in Al-Fe-Si-Mn-Mg Impact Extrusion Alloys Using Zirconium

ABSTRACT

A method of delaying the process of recovery of metals, a method to make an aluminum alloy comprising zirconium, and an apparatus comprising an aluminum alloy and zirconium are provided. In some embodiments, the aluminum alloy of can be formed from recycled aluminum alloys.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 62/698,612 filed Jul. 16, 2018, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a method of delaying the process of recovery of metals, a method to make an aluminum alloy comprising zirconium, and an apparatus comprising an aluminum alloy and zirconium. In some embodiments, the aluminum alloy of the present invention can be formed from recycled aluminum alloys.

BACKGROUND

Impact extrudable aluminum alloys can be formed into an apparatus. The apparatus, for example containers such as beverage containers or aerosol containers, can contain at least one coating. The coatings can be present on the internal portions of the apparatus, on the external portion of the apparatus, or on both the internal and exterior surfaces of the apparatus. Coatings can be cured at an elevated temperature in a furnace. The furnace can be an electric or gas furnace. The coatings can be cured at a temperature range that can be detrimental to the mechanical properties of the underlying as-extruded aluminum alloys. Specifically, the elevated curing temperature can decrease the yield strength and decrease tensile strength of the underlying as-extruded aluminum alloys. At these temperatures, mechanical properties of the as-extruded aluminum alloy can decrease as recovery in aluminum alloys is a thermally activated process. These temperatures precede recrystallization. In other words, the temperature required to cure the coating on an apparatus can decrease mechanical properties of the underlying aluminum.

SUMMARY

The present invention relates to a method to delay recovery in aluminum alloys by including zirconium in the alloy. When a metal is cold worked by a plastic deformation process such as impact extrusion, some of the mechanical energy expended to deform the metal is stored in the workpiece or apparatus. This stored energy resides at an atomic level in the structure of the metal as strain energy. Heating the workpiece or apparatus activates atomic diffusion processes, which begins to relieve the accumulated strain by microstructural and sub-microscopic rearrangements. With these microstructural and sub-atomic rearrangements, the properties of the workpiece or apparatus also change. “Delaying recovery” generally means delaying the onset of the process in which the strain energy stored in the metal due to a cold work process such as impact extrusion begins to be relieved. Generally, the recovery process precedes the process of recrystallization, which occurs at higher temperatures.

The aluminum alloy can be a pure or relatively pure aluminum alloy (i.e. not comprising recycled materials) or can be a recycled aluminum alloy. By including the zirconium, the mechanical properties of the aluminum alloy are maintained when the aluminum alloy is subjected to a temperature between about 220° C. and about 280° C. In some embodiments, the temperature can be about 240° C.

Advantageously, the inclusion of zirconium does not require other elements, including for example, silicon, iron, manganese and magnesium, to be added to the aluminum alloy in order to increase the mechanical properties of the alloy. Inclusion of these elements may be intended to compensate for loss of mechanical properties during exposure to the elevated temperature. Unfortunately, the addition of these elements can result in stronger alloys, which may be difficult to process or use to form certain shapes and configurations in articles of manufacturing. For example, an aluminum alloy comprising additions of these elements can result in an alloy that cannot be subjected to an impact extrusion process. Advantageously, the inclusion of zirconium does not increase the mechanical properties of as-extruded alloys, but instead prevents a lowering of these properties when subjected to elevated temperatures, for example temperatures required to cure coatings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a comparison of burst pressure for a material compared to the same material with zirconium.

DETAILED DESCRIPTION

An aspect of the invention is an aluminum alloy comprising between about 0.1 wt. % and about 0.15 wt. % of zirconium. The zirconium can be added to a recycled aluminum alloy. U.S. Pat. No. 9,663,846 and PCT Application No. PCT/US2016/069454 are directed to recycled aluminum alloys that can be used with the present invention. Each of these references are incorporated by reference in their entirety. The recycled aluminum alloys can be used to form an extruded container comprising zirconium of the present invention. The aluminum alloy composition of the present invention is provided in Table 1. All values are approximate.

TABLE 1 Element Minimum (wt. %) Maximum (wt. %) Nominal (wt. %) Si 0.1 0.4 0.15 Fe 0.25 0.5 0.31 Cu 0.05 0.2 0.09 Mn 0.07 0.65 0.41 Mg 0.05 0.75 0.49 Zn 0.005 0.25 0.05 Cr 0.005 0.20 0.05 Ti 0.005 0.05 0.01 Zr 0.05 0.15 0.15 Impurities 0.005 0.15 0.03 Al Balance Balance Balance

The present invention differs from other materials and compositions. For example, EP Patent Application No. 2881477, which is incorporated by reference, describes specific aluminum alloy compositions, in particular AA 1050, AA3102 or AA 3207. The components of these aluminum alloys can be found in the International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys (last revised January 2015) (available at http://www.aluminum.org/sites/default/files/TEAL_1_OL_2015.pdf). Between 0.05 and 0.2 wt. % of zirconium is added to these particular alloys. Notably, the amount of magnesium is limited to 0.1 wt. %. EP Patent 3075875, which is incorporated by reference, discloses the use of zirconium to raise the recrystallization temperature above 300° C. in an alloy that contains between about 0.1-0.5 wt. % Fe, 0.05-0.2 wt. % Si, less than 0.01 wt. % Mg, less than 0.01 wt. % Cu, less than 0.02 wt. % Zn, between 0.0-0.03 wt. % Ti, between 0.01-0.6 wt. % Mn, between 0.05-0.2 wt. % Zr, and the balance being aluminum. The present invention differs by requiring between about 0.1 wt. % and about 0.75 wt. % magnesium and between about 0.1 wt. % and about 0.15 wt. % zirconium. Other elements besides magnesium can also differentiate the present invention from EP 307875, including the weight percentage of copper. A second difference is that instead of utilizing a prime aluminum (i.e. not recycled), the present invention can be utilized with a recycled aluminum. In these embodiments, the amount of magnesium can be between about 0.05 and 0.75 wt. % of the recycled alloy containing zirconium.

U.S. Pat. No. 9,663,846 and PCT Application No. PCT/US2016/069454 disclose methods to form recycled aluminum alloys, and have been incorporated by reference in its entirety. The present invention can modify those methods by including zirconium into the liquid metal bath in sufficient quantities to increase the amount of zirconium in the alloy to between about 0.1 and 0.15 wt. %. To determine if enough zirconium has been added, samples can be taken from the molten metal and analyzed. The analysis can be performed on any suitable instrument, including a spectrometer, and the amounts of the materials adjusted accordingly. The zirconium can be pure zirconium (i.e. 100% Zr), or can be an ingot such that it is mixed with a second material. Suitable ingot materials include, but are not limited to, Zr—Al, Al—Zr, zirconium containing salt compounds, or combinations thereof. In some embodiments, Al—Zr masteralloy can include between about 5 wt. % and about 20 wt. % zirconium. Salts mixtures, for example potassium fluorozirconate (K₂ZrF₆) or compound zircon salts, such as CaF₂/LiCl/K₂ZrF₆, and also be used with the invention to provide zirconium to the material

Once the aluminum alloy comprising zirconium is formed, it can be made into a slug. U.S. Pat. No. 9,663,846 and PCT Application No. PCT/US2016/069454 describe methods for making a slug. Furthermore, the slug can be used to form a container using impact extrusion. Additional information about the impact extrusion process and the container can be found in PCT Application No. PCT/US2016/069454, which has been incorporated by reference in its entirety.

Examples

Samples were prepared wherein the material comprises about 25 wt. % recycled aluminum (the balance being non-recycled aluminum), while other samples were prepared comprising the 25 wt. % recycled aluminum and zirconium (the balance being recycled aluminum). Table 2 below includes the compositions of the samples.

TABLE 2 Alloy Si Fe Cu Mn Mg Cr Zn Ti B V Zr ReAl25 0.12 0.26 0.00 0.21 0.19 0.00 0.00 0.01 0.002 0.001 ReAl25 + 0.118 0.279 0.00 0.211 0.156 0.00 0.0.3 0.018 0.116 Zr The ReAl25 can include up to about 0.2 wt. % impurities, with the remaining balance of the material being aluminum. Using these materials, the effect of thermal curing on the burst pressure was determined after thermal curing at a temperature of approximately 240° C. Table 3 provides the burst pressure of samples before thermal curing and after thermal curing.

TABLE 3 Burst Pressure (bar) Before Thermal After Thermal Alloy Curing Curing Difference ReAl25 26.4 25.0 −1.4 ReAl25 + Zr 26.4 26.2 −0.2 Table 3 illustrates that the ReAl25 with the zirconium delays the process of recovery compared to the ReAl25 sample. Table 4 provides the burst pressure for multiple samples of ReAl25 and ReAl+Zr samples.

TABLE 4 Burst Pressure (bar) Sample ReAl25 ReAl25 + Zr 1 24.6 26.5 2 25.1 25.9 3 24.6 26.5 4 24.7 26.2 5 24.8 26.1 6 24.3 26.4 7 25 26 8 25.2 26.5 9 24.6 26.4 10 25.3 26.2 As illustrated in Table 4, ReAl25+Zr alloy maintains as-extruded mechanical properties after thermal curing, effectively delaying the process of recovery during thermal curing. In contrast, the as-extruded mechanical properties of ReAl25 after thermal processing have decreased, the process of recovery has commenced. FIG. 1 illustrates a graphical representation of the data in the Table 3. The same process conditions (tooling, preform dimensions, process parameters and curing temperatures) were used. The only change was the alloy.

Ranges have been discussed and used within the forgoing description. One skilled in the art would understand that any sub-range within the stated range would be suitable, as would any number within the broad range, without deviating from the invention.

The foregoing description of the present invention, related to an aluminum alloy comprising zirconium to delay the recovery of the aluminum alloy, has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiment described hereinabove is further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art. 

1. A method to form an aluminum-zirconium alloy, comprising: providing a scrap metal comprised of at least one of a 3104, a 3004, a 3003, a 3103, 3013 and a 3105 aluminum alloy; blending said at least one of said 3104, said 3004, said 3003, said 3013, said 3103, and said 3105 aluminum alloy with greater than 40 wt. % of a 1000 series aluminum alloy, and a zirconium containing material to form a recycled aluminum alloy melt; casting said recycled aluminum alloy melt to form a slab; hot rolling the slab to reduce a thickness of the slab and produce a hot milled slab; and cold rolling the hot milled slab to reduce a thickness of the hot milled slab to produce a milled strip comprising the aluminum-zirconium alloy.
 2. The method of claim 1, further comprising: punching the milled slab to create a slug from the milled slab; deforming said slug comprised of said recycled aluminum alloy into a preferred shape in an impact extrusion process to form a shaped container adapted to receive an end closure.
 3. The method of claim 1, further comprising blending titanium boride with the recycled aluminum alloy melt.
 4. The method of claim 1, wherein a thickness of the slab is between about 20 mm and about 35 mm.
 5. The method of claim 1, wherein a thickness of the hot milled slab is between about 6 mm and about 10 mm.
 6. The method of claim 1, wherein a thickness of the milled strip is between about 3 mm and about 10 mm.
 7. The method of claim 1, wherein the zirconium containing material is selected from the group consisting of a Zr, a Zr—Al, a Al—Zr, a zirconium salt, K₂ZrF₆, CaF₂/LiCl/K₂ZrF₆, and combinations thereof.
 8. An aluminum alloy used in a slug for an impact extrusion process to form a metallic container, which is configured to receive an end closure, the aluminum alloy comprising: at least about 97 wt. % Al; at least about 0.10 wt. % Si; at least about 0.25 wt. % Fe; at least about 0.07 wt. % Mn; at least about 0.05 wt. % Mg; at least about 0.1 wt. % Zr; at most about 0.15 wt. % impurities; and a balance comprising at least one of Cu, Zn, Cr, and Ti.
 9. The aluminum alloy of claim 8, wherein the aluminum alloy further comprises: no greater than about 99.31 wt. % Al; no greater than about 0.4 wt. % Si; no greater than about 0.5 wt. % Fe; no greater than about 0.2 wt. % Cu; no greater than about 0.65 wt. % Mn; no greater than about 0.75 wt. % Mg; and no greater than about 0.15 wt. % Zr.
 10. A metallic container, comprising: a body of the container with a diameter between about 0.86 inches and about 3 inches, a height between about 2.3 inches and about 8.5 inches, and a thickness of a wall between about 0.003 inches and about 0.16 inches; wherein a material of the container comprises: at least about 97 wt. % Al; at least about 0.10 wt. % Si; at least about 0.25 wt. % Fe; at least about 0.07 wt. % Mn; at least about 0.05 wt. % Mg; at least about 0.1 wt. % Zr; at most about 0.15 wt. % impurities; and a balance comprising at least one of Cu, Zn, Cr, and Ti; and a coating, wherein the coating is applied to at least one surface of the body of the container, and wherein a burst pressure of the container is between about 25.4 and 26.6 bars after thermal curing the coating.
 11. The container of claim 10, further comprising an end closure.
 12. The container of claim 10, wherein the material of the container comprises: between about 0.07-0.2 wt. % of Si; between about 022-0.38 wt. % of Fe; between about 0-0.13 wt. % Cu; between about 0.11-0.61 wt. % of Mn; between about 0.13-0.73 wt. % of Mg; between about 0.1-0.15 wt. % Zr; between about 0.02-0.07 wt. % of Zn; between about 0-0.03 wt. % of Ti; between about 0-0.15 wt. % of impurities; and the balance of Al.
 13. The container of claim 10, wherein the burst pressure of the aluminum-zirconium alloy is greater than about 7% of a burst pressure of an aluminum alloy without zirconium. 